Yeah, right if you give all 20MHz to one sector, but in the real world the most cost efficient configuration is a 3 sector base station (covering full 360 deg) and you need seperate spectrum for each sector otherwise you get massive cross sector interference which will reduce your throughput to a trickle.
added that operators can do compression, modulation and other things to make sure the spectrum is used efficiently.
WiMAX is standards based, hacking the equipment to operate out of spec is counter to its objective of being cost effective by virtue of common multi-vendor competition.